1. Technical Field
This invention relates generally to the making of powder metal gears, and more particularly to the cutting and densifying of the gear teeth.
2. Related Art
U.S. Pat. No. 4,708,912 discloses a method of manufacturing powder metal gears in which a sintered metal gear blank is mounted in a rolling machine for rotation about a first axis between a set of adjacent toothed rolling tools which are each mounted for rotation about second and third axes that are parallel to the first axis of the gear blank. Densification takes place through displacement of the gear blank material by the teeth of the rolling tools. The gear blank can be provided with preformed teeth which are subsequently densified by the rolling tools.
U.S. Pat. No. 5,711,187 discloses a method of densifying powder metal gears wherein a powder metal gear blank is mounted for rotation about a first axis adjacent a toothed rolling tool mounted for rotation about a second axis which is parallel to the first axis. The blank and tool are moved relatively toward one another to displace and densify the material of the gear teeth. The manner in which the teeth of the gear blank are pre-formed for subsequent densification is not disclosed.
It is an object of the present invention to simplify the manufacture of powder metal gears having densified gear teeth.
A method of manufacturing a powder metal gear according to a presently preferred embodiment of the invention comprises compacting and sintering powder metal to form a gear blank which is then supported for rotation about a first axis. A tool is supported for rotation about a second axis which is transverse to the first axis of the gear blank. A tool has a series of gear teeth cutting portions and a set of axially adjacent gear teeth surface densification portions. The tool is driven about the second axis and the gear tooth cutting portions are brought into engagement with the gear blank whereby teeth are cut into the gear blank through the removal of gear blank material to prepare a toothed gear blank. Without dismounting either the tool or toothed gear blank, the tool and the toothed gear blank are shifted relative to one another to bring the gear toothed surface densification portions of the tool into meshed engagement with the teeth of the toothed gear blank and the tool driven about the second axis to displace and densify the surface the gear teeth.
The invention has the advantage of providing a simple method for manufacturing powder metal gear teeth.
The invention has the further advantage of providing a method of forming powder metal gear teeth with great precision and repeatability, since both the cutting and densification features are provided on the tool and their position and movement controlled according to the invention such that they are presented to the gear blank without disturbing the fixtured relationship of the tooling gear blank. In other words, by combining the cutting and densification steps into a single operation using the tool with both cutting and densification features, greater control over the dimensional and physical properties of the resultant densified powder metal gear is achieved.